A typical organic light-emitting device includes a hole injection anode layer, an active light-emitting zone comprising one or more electroluminescent organic material(s), and a cathode. One of the electrodes is optically transmissive while the other one is optically reflective. The function of the anode layer is to inject positively charged particles, referred to as holes, into the light-emitting zone, and that of the cathode is to inject electrons into the emission zone. A process involved in the recombination of the electrons and the holes leads to the creation of light wave. The light wave is escaped through one of the aforementioned electrodes.
U.S. Pat. No. 4,356,429 discloses inserting a hole-transport organic layer between the anode and the emission zone, and an electron-transport organic layer between the cathode and the emission zone.
As molecules are perfectly structured so that there is no “intrinsic” charge, i.e. extra charge, in the molecules. All charges have to be injected from the electrodes during device operation. It is well known that regulated hole injection is critical to OLED device performance (Shih-Fang Chen and Ching-Wu Wang, Applied Physics Letters Vol. 85, 765 (2004)). A great amount of work has been conducted to find suitable hole injection method.
U.S. Pat. No. 4,539,507 disclose a hole injection zone to improve power conversion efficiency. United States Patent Pub. No. US2003/0117069 A1 discloses the use of crystalline CuPc film as a hole injection layer. U.S. Pat. No. 6,208,077 B1 discloses the use of a thin non-conductive fluorocarbon polymer film in the hole injection zone. U.S. Pat. No. 6,198,218 B1 discloses the use of diamond film as a hole injection layer. U.S. Pat. No. 5,710,484 discloses the use of sputtered carbon film as a hole injection layer. The use of small organic molecular film as a hole injection layer can be found in the following patents: U.S. Pat. No. 5,998,803; PCT patent WO 2004/068912 A1; US patent pub. No. 2003/0015723 A1; PCT patent No. WO96/22273.
As a family member of naturally occurring allotropes of carbon, fullerene materials are known for their robust structures and superior charge transport properties. U.S. Pat. No. 5,861,219 discloses the use of fullerenes as a dopant added to a host metal complex of 5-hydroxy-quinoxaline used in organic light emitting diodes. The host metal complex of 5-hydroxy-quinoxaline is contained in the electroluminescent layer which forms the emission zone in the structure. United States Patent Publication US 2002/0093006 A1 discloses the use of a fullerene layer as the light emissive layer in an organic light emitting diode structure.
United States Patent Publication US 2003/0042846 A1 discloses the use of a fullerene layer as an electron acceptor layer in organic photovoltaic devices.
Japan Patent 3227784 and Japanese patent application 04-144479 disclose the use of fullerenes as a hole transport layer.
U.S. patent application Ser. No. 10/811,153 discloses the use of fullerenes in an electron transport layer.
U.S. Pat. No. 5,171,373 discloses the use of fullerenes in solar cells. U.S. Pat. No. 5,759,725 discloses the use of fullerenes in photoconductors.
The use of fullerenes as a hole blocking interface layer between the hole transport layer and the light emission layer has been disclosed by Keizo Kato, Keisuke Suzuki, Kazunari Shinbo, Futao Kaneko, Nozomu Tsuboi, Satosh Kobayashi, Toyoyasu Tadokoro, and Shinichi Ohta, Jpn. J. Appl. Phys. Vol. 42, 2526 (2003).